The U.S. Census Bureau


Census 2000 New Census Block Strategy

Census Block Number and Collection /Tabulation Strategy for Census 2000

The Census Bureau has proposed a new census block number format and collection/tabulation block strategy for Census 2000. For further information contact Noelle Joll or Jamie Rosenson, Bureau of the Census, Geography Division, Washington, DC 20233, telephone: (301)457-1099.

If sending comments by e-mail, please include a phone number, street address, and information regarding your professional/organizational affiliation.

We are maintaining two sets of block numbers, one for collection and one for tabulation.

By maintaining separate sets of block numbers for collection and tabulation, we can renumber blocks for tabulation to recognize changes to the feature pattern; we also can eliminate situations that resulted in the creation of "sliver" census tracts for the 1990 census. The introduction of an independent numbering cycle for tabulation will allow us to assign additional block numbers to blocks formed by new features that were discovered during our enumeration activities. In addition, the use of separate block sets for collection and tabulation will enable us to better serve the participants in our statistical area programs (such as those programs for census tracts, block groups, and census designated places), and provide an opportunity for our local participants in these programs to verify the plans they submit for these areas. Boundaries defined by local participants for statistical areas will better reflect the most recent feature changes to fast-growing areas.

We are expanding the block number by numbering collection blocks within county with a 4- or 5-digit numeric identifier, and by numbering tabulation blocks within census tract and block group with a 4-digit numeric identifier.

For Census 2000, collection blocks will be numbered within county with either a 4- or 5-digit numeric identifier, depending on feature requirements within the county. Only those data users working with the Census Bureau on the precensus activities will encounter collection blocks. Tabulation blocks will be numbered within census tract and block group with a 4-digit , all numeric identifier. The 1990 3-digit block number format imposed serious restrictions on the number of separate polygons that could be identified as blocks because we were limited to 97 available numbers for each block group. At least 1,000,000 potential blocks were not identified as such because of the 3-digit block number format limitation. By expanding the block number, we will remove the arbitrary constraint on the numbering process. We will create more blocks, allowing us to provide more data at the census block level for various tasks including U.S. Congressional and state house/senate redistricting and defining school districts.

Because census blocks provide a statistical framework for a variety of Federal, state, and local programs designed for such purposes as transportation planning or providing rural services, persons served by these programs will benefit as well. These changes allow the Census Bureau to associate water polygons with a surrounding land block (for both collection and tabulation operations), thereby allowing individuals preparing equivalency files to make a more precise assignment of water.

Census Block Relationship Files will Link the 1990 Blocks to the 2000 Blocks

The Census Bureau will create census block relationship files for participants in Census Bureau programs and for data users. We will prepare the following files to meet these needs:

The Census Bureau has produced Census 2000 Block Relationship Files on the basis of one-to-one, one-to-many and many-to-one block(s). The purpose of the relationship files is to show how 1990 census blocks now relate to Census 2000 blocks. The relationship files contain a part flag field. A value of "p" in this field identifies blocks that do not have a whole block to whole block relationship. They do not depict the actual spatial relationships between census blocks. The actual areal relationships between blocks can be determined using commercially available GIS software and publicly available versions of the Census Bureau’s TIGER/Line files.

The Census Bureau organized its address list for review by tribal and local government liaisons before Census 2000 (under Public Law 103-430) using the collection block numbers; we provided the 1990 tabulation block number for each address in addition to the collection block numbers. The Census Bureau is confident that these changes relating to block numbers and the separation of collection geography from tabulation geography will provide an improved and more accurate geographic data base, and that the relationship files described above will facilitate operations for local participants in our Census programs.




Source:  U.S. Census Bureau
Last Revised: Thursday, 29-Aug-2002 11:20:52 EDT